Question

A torch bulb is rated $5V$ and $500mA$.

Calculate its c.energy consumed when it is lighted for 4 hours

Answer 1

Step 1- Given data and formulas

1. Applied voltage $V=5V$
2. Current through the bulb $I=500mA$
3. The time for which the bulb is lighted $t=4h$

The electric power is given by,

$P=VI$

where $P$ is electric power.

Note: $1mA={10}^{-3}A$ and $1h=3600s$

Step 2- Finding the power

Substitute the known values into the formula.

$$\begin{gathered} P=5V\times 500\times {10}^{-3}A \\ P=2.5W \end{gathered}$$

Step 3- Finding the energy consumed

The energy consumed in a certain time is given by

$E=Pt$

where $E$ is the energy consumed,

Substitute the value of time and power into the equation to find the energy consumed.

$$\begin{gathered} E=2.5W\times 4\times 3600s \\ E=36000J\times \frac{1kJ}{1000J} \\ E=36kJ \end{gathered}$$

Thus, the energy consumed when it is lighted for 4 hours is $36kJ.$